1. Field of the Invention
The present invention pertains to achieving optimal quality when transmitting voice data over a lossy network; more particularly, it pertains to managing jitter buffering of data packets over a packet-switched network.
2. Related Art
Latency and jitter are important aspects of network performance that can degrade communication between any two points on a packet-switched network, like the Internet. Latency is the delay introduced on packets during travel from one site to another. Latency will be perceived by the end users as a delay in the response of the remote site. Jitter is the variation in latency from one packet to another.
Latency and jitter each impact communication differently. F or example, if packets always arrived 50 milliseconds (ms) after being transmitted, then there would be a 50 ms latency and no jitter. In another example, however, if packet #1 arrived 100 ms after transmission, packet #2 arrived 50 ms after transmission, and packet #3 arrived 150 ms after transmission, there would be an average jitter of +/xe2x88x9233 ms. In voice over Internet protocol (VoIP) applications, jitter is more critical than latency. Jitter can cause a packet to arrive too late to be useful. The effect is that the packet may be delayed enough that the end user will hear a pause in the voice that is talking to them, which is very unnatural if it occurs during the middle of a word or sentence.
Jitter typically occurs when the network utilization is too high, and packets are being queued, causing delivery times to become unpredictable. The Internet, because of its complex structure, is often subject to varying degrees of jitter. Jitter variation can occur at different locations and at different times depending upon network traffic and other conditions. Thus, jitter needs to be managed.
Effective jitter management is especially needed in VoIP applications. Each VoIP call needs jitter management. FIG. 1 shows an example VoIP architecture 100, including gateways 110, 120 that provide an interface between public-switched telephone networks (PSTN) 130, 140 and a packet-switched network 102. A voice call is carried out between telephone 150 and telephone 160 through PSTN 130, gateway 110, network 102, gateway 120, and PSTN 140.
Static jitter buffering is one conventional technique to compensate for jitter. As shown in FIG. 2, static jitter buffering is carried out in gateway 120 which receives voice packets from network 102. A static jitter buffer 220 is provided to buffer the received voice packets from network 102. In such static jitter buffering, however, there is a compromise between the size of the jitter buffer and the delay of voice packets waiting in the jitter buffer. In particular, if the jitter buffer is large, it accommodates greater variation in jitter. The output packet traffic may not be jittery, but noticeable delays occur. If the jitter buffer is small, the delay is smaller but gaps in traffic are not accommodated.
A method, system, and computer program product is provided that manages jitter in packet-switched networks. In one embodiment, the present invention manages jitter in a VoIP system that includes a framer, a traffic analyzer, and a jitter manager. The framer time-stamps incoming packets and discards out-of-order packets. The framer outputs the in-order packets to the traffic analyzer and the jitter manager. The traffic analyzer maintains a sliding window array of a set of packets for use in calculating jitter statistics. These statistics are sent from the traffic analyzer to the jitter manager. The jitter manager uses these statistics to manage the flow of packets, the insertion or discardation of silence packets, and the supervision of any connected jitter buffers.
Handling jitter comes at the expense of latency, however, since the only way to handle jitter is to buffer additional data. So that when the data arrives exceptionally late, continuous playback to the end user can be maintained. Yet, the present invention manages the jitter buffer""s size so that the latency does not grow too long. In this way, the present invention compensates for network jitter without resorting to excessive buffering.
Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.